Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffolding, functioning to physically hold open and, if desired, to expand the walls of affected vessels. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once at the desired locations. Examples in the patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for local administration of therapeutic substances at diseased sites. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.
One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition (also referred to as a coating substance) including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.
The process of medicating a stent generally comprises repeatedly coating the stent with various layers of composition. For quality assurance purposes, after each coating application, the stent is weighed to determine if the amount of composition applied is within parameters. If too much composition was applied, then the stent can be discarded. If too little composition was applied, then another layer can be applied.
Conventionally, the step of weighing is accomplished by placing the stent onto a balance and manually entering the weight into a spreadsheet program. The spreadsheet program can then calculate the difference between two consecutive weight measurements made before and after a layer application to calculate the weight of the layer. Based on this calculation, an operator can choose to discard the stent, reapply the coating layer, or continue the process, such as applying other coating layers. However, because it requires manual data entry after each application of a coating layer, this method is time consuming and prone to data input errors. Additionally, each time the operator handles the stent, a risk of causing damage to the coating exists.
Accordingly, a new system and method is needed that substantially reduces data input errors and the time associated with the fabrication process as well as risks associated with the operator handling of the stent.